1. Field of the Invention
The invention is directed to a method for the mechanical alloying of brittle and hard materials, a planetary mill for the mechanical alloying of brittle and hard materials and the use of a planetary mill for the mechanical alloying of brittle and hard materials.
2. Description of Related Art
The mechanical alloying of powdery or granular materials to each other has been known for a long time. For this purpose, the materials to be alloyed to each other are placed in a vessel together with preferably ball-shaped (grinding) bodies. Then, the vessel is moved in such a manner that the bodies mix and comminute the materials to be alloyed and by their impact destroy the structure of the different materials to such an extent that an alloy is formed. Thus, mechanical alloying is based on deformation of the materials to be alloyed. Originally, mechanical alloying processes were restricted to ductile materials, such as metals, whose chemical bond is largely of a metallic character. Because of their relatively easy moldability, such ductile materials can be readily alloyed in a mechanical manner, wherein the alloying process can be understood as a kneading connection. Hard and brittle materials, e.g. germanium and silicon, were alloyed for the first time in the Eighties. For alloying such hard and brittle materials, considerably more energy has to be applied than in case of ductile materials. To perform mechanical alloying, there are used so-called vibratory mills wherein the materials to be alloyed (grinding stock) along with grinding bodies are filled into a vessel which is then subjected to vibration. The articles "Mechanical Alloying of Brittle Materials" by R. M. Davis, B. McDermott and C. C. Koch, Metallurgical Transactions A, 1988, Vol.19A, pp. 2867 to 2874 and "The Physics of Mechanical Alloying: A First Report" by D. R. Maurice and T. H. Courtney, Metallurgical Transactions A, 1990, Vol. 21A, pp. 289 to 303, deal with research in the physical aspects of mechanical alloying of hard and brittle materials. For industrial applications of mechanical alloying processes for brittle and hard materials, vibratory mills are less suited because the charges to be processed are too small. In this regard, so-called planetary mills offer better conditions. A planetary mill comprises a first disk (a so-called sun wheel) which is rotatingly driven. On the circumference of the sun wheel, a plurality of (smaller) likewise rotatable second disks (so-called planetary wheels) are rotatably supported. On the planetary wheels, grinding drums are arranged. Up to now, planetary mills of the above type have been used for the comminuting and dispersing of materials, wherein the materials to be processed, i.e. the grinding stock, are placed into the grinding drums together with freely floating grinding bodies (grinding balls). The commercially available planetary mills operate with fixed, unchangeable speed ratios between the grinding drum and the sun wheel and are not useful for the mechanical alloying of brittle and hard materials because the effect of the grinding bodies on the materials to be alloyed is insufficient. Although the article "Broyeurs a satellites" by Albert Joisel, Revue des materiaux de construction, Nr. 493, 1952 describes research directed to the energy input for the grinding bodies of a planetary mill, this research did not yet lead to consequences for the practical use of a planetary mill for mechanical alloying.
It is an object of the invention to provide a method and a device which are adapted for the mechanical alloying of brittle and hard materials by use of a planetary mill.